DESCRIPTION (Based on the applicant's abstract): The developing nervous system is one of the most sensitive potential targets of environmental toxins. Relatively small changes in neuronal pathfinding or connectivity may lead to significantly abnormal neuronal wiring patterns, which in turn may cause behavioral abnormalities. This proposal will use cell cultures of N1E-115 neuroblastoma cells and rat hippocampal pyramidal neurons as models for neuronal development. The proposed research will focus on the interference of selected neurotoxins with the normal function of VSCC, (Ca++)i homeostasis, and the neuronal cytoskeleton. Four interrelated hypotheses will be investigated. 1. Alterations in Ca++ influx or extrusion, leading to changes in (Ca++)i, play major roles in regulating neurite growth. Ca++ influx through L-type channels is required for both neurite initiation and growth cone motility, but not for neurite elongation. Specific Ca++ channel antagonists will be applied to neuronal cultures to determine the importance of L-type Ca++ channels to growth cone motility, neurite initiation, and both short- and long-term neurite elongation. A fura-2 based Ca++ imaging system with extreme sensitivity and high spatial resolution will be used to assess the effects of Ca++ channel antagonists on the distribution of(Ca++)i within differentiating neurons. 2. Lead ion (Pb++), cadmium ion (Cd++), permethrin, and 1,1-bis(p-chlorophenyl)-2,2,2-trichloromethane (DDT) may alter influx into vertebrate neurons, through actions on Ca++ or sodium ion (Na+) channels. The effects of these toxins will be studied by voltage-clamp techniques. 3. Triethyl lead, methyl mercury, permethrin, and DDT may raise (Ca++)i through their actions on membrane potential, cellular energy production, specific membrane channels and/or Ca++ extrusion pumps. (Ca++)i will be measured after acute and chronic exposure to these substances. 4. The Pb++, Cd++, triethyl lead, methyl mercury, permethrin, and DDT may interfere with the development of the nervous system by inhibiting neurite initiation and growth cone motility. These neurotoxic effects are probably mediated, at least in part, by disruption of (Ca++)i homeostasis. The applicant will correlate neurite growth, effects on Ca++ channels, and (Ca++)i in cultured neurons with and without toxin exposure.